In the cigarette industry, modern manufacturing techniques have increased production speeds to the point that manual quality control methods are no longer adequate. One area in which this problem exists is in filter rod manufacturing. The filter tip on the common filter-tipped cigarette is actually a short segment of a longer (e.g. 100 mm.) filter rod which is cut into pieces in the final stages of the manufacture of the cigarette. One rod normally provides filter tips for up to six cigarettes. These filter rods are manufactured on high-speed filter-making machines at a rate of up to 4,000 per minute per machine.
In the filter rod manufacturing process, the manufacturing parameters which must be under closest quality control are the pressure drop and circumference. These two parameters are highly interdependent, and often repeated adjustment of the filter-making machine is required before the manufactured rods can meet specifications.
Pressure drop may be thought of as the resistance to flow of the gas stream through the filter, and it affects both the "draw" of the cigarette and the tar and nicotine removal efficiency of the filter. Circumference is important because manufacturing uniformity must be maintained in the cigarette product (the tip will be attached to a tobacco rod of controlled circumference) and because of its effect on pressure drop. If the material is packed tightly into a smaller circumference rod, the result will be an increase in the pressure drop.
Previously, the method for ascertaining quality in filter rod manufacturing was as follows: a quality control technician manually sampled the production of each filter-making machine and carried the samples to a manual measuring device. This measuring process took as much as ten minutes to perform, during which time as many as 240,000 individual filters could be manufactured on each machine. If a filter-making machine needed adjustment during this period, many hundreds of dollars of production could be wasted.
In the past several years, both cigarette manufacturers and filter material suppliers have made attempts to produce an automatic rod test method. Improvement in measurement and material handling techniques have been successfully made, but effective computer implementation has not, as far as is known, been achieved prior to the present invention.
Some of the improvements referred to above are contained in U.S. Patent and Trademark Office Public Disclosure No. T938010 which describes and shows a partially automated rod test station. Although the unit as described in that publication is automated insofar as automatically transporting the filter rod through the test sequence, thus reducing the time required to handle the rod, the pressure drops in the pressure drop gauge and circumference gauge are detected by manometers which are inherently sensitive to temperature and barometric pressure changes and to human error in reading the gauges. Although precision components may be used in the vacuum system for the pressure drop gauge and pressure system for the circumference gauge, such systems nonetheless require frequent calibration and like the manometers are subject to drift as ambient conditions may change.